This invention relates to an automatic grinding apparatus used for finishing a welded excess metal deburring or chamferring a work piece.
An automatic grinding apparatus for finishing the welded excess metal, deburring or chamferring the work piece is known from Japanese Patent Application Laid Opened No. Hei 1-121169, for example, such as the apparatus comprising an electronic grinder of which a motor load current decreases or increases due to the metal removal quantity per unit hour, a slider supporting the grinder, a sliding device elevating the slider, a travelling truck and rails. Said travelling truck runs parallel to a grinding line (of the excess metal of or its reinforcement of weld) on the rails at a constant speed. In said apparatus, a pinion is projected from the bottom of the travelling truck to engage a rack provided on the guide rails. A travelling motor which is contained in the travelling device rotates the pinion through a speed reduction device to run the truck toward a longitudinal direction of rails at a constant speed. The sliding device controls the distance in a perpendicular direction between the electronic grinder and the excess metal of the welding, in which a supporting block contained in the slider is threaded to engage an output shaft of the slide elevation motor which on the upper end of the device to elevate the slider by a rotation of the elevation motor. The electronic grinder is attached by a holder provided at the front portion of the slider.
When the truck travels at a constant speed along the grinding line (of the excess metal of the welding), the slide device is so controlled that the motor load current of the grinder is constant. As a result, the metal removal rate in 3 mm/min is always kept constant even if the grinding disk is worn. Therefore, in the case that the excess metal having a cross section as shown in FIG. 8, substantially equally exists on the welding line as shown in FIG. 9, even if a base metal surface is deformed, the equally finishing over such deformed surface is performed. Further since the apparatus is had no effect of a gravity as required in a system for controlling the grinding pressure, there is an advantage that the controlling capacity is stable for any type of grinding attitudes such as facing towards the horizontal direction or overhead direction.
While in actuating the above described apparatus at the grinding initiation, it is required to start the rotation of the grinding motor in a condition that the grinding disk does not contact the object to be ground and thereafter either of three operating system described hereinbelow will follow:
(A) To start both of the slide controlling circuits (not shown) and the travelling truck simultaneously.
(B) To start only the slide controlling circuit at first and then the travelling switch is operated at the time of the grinding process being started after the sliding device is automatically lowered due to the low grinding motor load current.
(C) To lower the sliding device by switch operation, then the start both of the sliding controlling circuit and the travelling truck at the time of the grinding process being started.
In the above described system, (A) is automatically actuated by an external command, however the unground portion remains near around the grinding initiation. (B) and (C) are utility systems in which there remains no unground portions, however the switch control requires a monitor by a person.
In the above described travelling truck system, since the actuation of the system at the grinding initiation has originally depended on the person, it is not a great problem that the monitoring is required. While for grinding a plurality of portions of the welding excess metal is by a program control in which a robot is used for the travelling device, since the system is also automatically actuated at each grinding initiation by an actuation signal, the residual phenomenon of the unground portion is inevitable in a conventional system. In case of grinding the wholepart of welding excess metal to the extent of grinding to the ridgeline thereof, it is also inevitable that the grinding disk comes into collision with the object to be ground when the robot reaches to the next grinding initiation, since the sliding device falls down at said ridgeline by a slide control faculty.
In addition, when the robot reaches the next grinding initiation after the new grinding disk is exchanged since the sliding device has been automatically lowered due to the exhaustion of the grinding disk, it is also inevitable that the new grinding disk comes into collision with the object to be ground. Further when the grinding motor is stopped during grinding condition to finish the grinding process, the rinding disk intrudes into the object to be ground due to an inertia rotation of the motor, and the base metal surface is subject to be damaged.
The object of the present invention is to provide an automatic grinding apparatus improved in preventing the grinding disk to come into collision with, or to intrude into the object to be ground, or to damage the base metal surface in case that a robot is used as the travelling device for a constant rotating grinder.